This invention relates to flexible polyurethane foams, more particularly to flexible polyurethane foams which exhibit excellent flame resistance in small scale burn testing. The terms "combustion-modified," "flame resistant" and similar terms as used herein refer to a material's performance in laboratory flammability tests, and are not meant to describe performance under actual fire conditions.
Flexible polyurethane foams are widely used as cushioning material in, for example, furniture, automobile seating, impact-reducing medias, and the like. One concern regarding the use of these foams is their performance under fire conditions, particularly their ability to resist igniting and to extinguishing themselves when exposed to flame.
Many attempts have been made to reduce the flammability of polyurethane foams. The most common method is to incorporate a halogenated compound or phosphate ester flame retarding agent into the foam formulation. These agents have been somewhat successful in reducing the flammability of the foams. However, the use of these flame retarding agents has several substantial drawbacks. Although they are somewhat successful in suppressing flames, under fire conditions they decompose to form toxic gases, particularly gaseous halogen-containing compounds such as HCl and HBr. Foams containing these agents, although they resist flames, sometimes smolder during fires. In preparing the foams, the halogenated flame retarding agents often discolor the interior of the foam, and/or lead to degradation of the foam properties. In addition, these flame retardants deactivate many of the catalysts used in foam formulations. Moreover, many companies do not like to introduce halogenated compounds into the workplace for fear of worker exposure. In addition, relatively large quantities of these agents must be used in order to obtain satisfactory results, adding significantly to the cost of the foam.
Other types of flame retardant additives are described in U.S. Pat. No. 4,722,942, which discloses the use of fire retardant additives comprising hydroxyl-terminated alkanes having a plurality of primary hydroxyl groups and alkylene ethers and polyethers having a plurality of primary hydroxyl groups. However, the primary hydroxyl-containing compounds described above are often incompatible with the high molecular weight polyols used in the preparation of polyurethane foams. In addition, such primary hydroxyl-containing compounds may also restrict cell-opening during the manufacture of the foam.
In view of the foregoing, it would be desirable to provide a polyurethane foam containing a flame retarding additive which does not release halogen-containing gases when burned, which does not present the processing and exposure problems associated with the halogenated and phosphate ester agents, and which is compatible with the high molecular weight polyols used in the preparation of polyurethane foams.